1. Field of the Invention
The present invention relates to tape drive systems and data storage tape cartridges.
2. Background Art
Data storage tape drives and data storage tape cartridges are generally available in two types. In one type, tape guides are provided internal to the tape cartridge for guiding the tape along a defined tape path. A second type of tape drive has tape guides that are provided within the drive that are external to the cartridge.
Internal tape guides tend to be subject to lateral tape motion that may limit tape storage capacity. Lateral tape motion is one part of an overall drive and tape cartridge system tolerance stack-up. The mechanical system stack-up is combined with system responses and corrections, such as the responsiveness of the actuator, the ability of the heads to read partial tracks, lateral tape movement, amplitude and frequency relative to tape speed, and the like, that determine the full track mis-registration budget. Track mis-registration budgets accommodate a limited degree of tape mis-registration by allowing for additional space between adjacent tracks on a tape. Track mis-registration budgets are determined based upon full tape drive and tape cartridge tolerance stack-up. Tape speed and actuator performance characteristics also impact track mis-registration budgets. As the track mis-registration budget for a tape drive system increases, less data may be stored on each tape cartridge which reduces storage efficiency. Problems with lateral tape motion are inherent in all internally guided tape cartridges.
Servo off tracks are a result of the read/write head not being able to follow lateral tape movement adequately. Servo elements follow a pattern written on the tape that are provided next to the read/write elements. When the actuator cannot keep up with the lateral tape movement of the tape, the servo elements read off of the servo pattern written on the tape which results in a servo off track.
Externally guided tape cartridges generally require threading the tape through the external tape guides. External tape guides provided within the tape drive allow closer tolerances to be held and allow for greatly reduced track mis-registration budgets. Problems associated with externally guided tape drive systems include difficulty in threading the tape through the system, exposure of the tape when it is external to the cartridge to foreign matter, and possible damage to the tape when it is guided outside of the tape cartridge. In addition, the time required to thread the tape is too long to be competitive in the fast access drive/cartridge market.
Fast access tape cartridges may be presented to a tape drive system with one half of the tape on each of two tape reels. Access is faster because less than half of the tape must be reviewed to locate the desired data. Access can also be faster with internally guided tape cartridges because it is not required to thread the tape. For example, the time to data may be as low as four seconds with a cartridge, while a drive guided system may require ten seconds just for threading the tape. There is a need for fast access tape drive systems that can provide more tape path options. In fast access tape drive systems the use of thinner media and more stringent tape path requirements are difficult to achieve with current internally guide data storage tape cartridges. Externally guided tape systems cannot use this approach for providing fast access to data.
There is a need to extend the life of current tape drive systems to allow them to store more data more efficiently. It would be advantageous to increase the storage capacity of current and future data storage cartridges by improving tape registration. To the extent that lateral motion can be more closely controlled, additional data may be written to data tape storage cartridges.
These and other problems are addressed by applicant's invention as summarized below.